There are new change detection capabilities released on IMAGINE Objective in 9.3 and more in IMAGINE Professional in 2010 (coming this fall). Or you can create your own in the Model Maker. This graphical spatial modeler was introduced in 1993. It is being expanded in ERDAS IMAGINE 2010. ESRI's Model Builder is a knock-off of IMAGINE Model Maker. Ref: http://field-guide.blogspot.com/2009/04/brief-history-of-erdas-imagine.html.